In some high power inner focusing zoom lens, a displacement of a focusing lens during the photographing at the minimum object distance is greatly varied depending upon a zoom ratio, and hence, even if an attempt to enhance a photographing performance at the minimum object distance within a single stroke of focusing cams is successful in one of zooming ranges, this resultantly causes the displacement of the focusing lens being elongated in the remaining zoom ranges, which brings about the so-called “varying focal” length. For focusing cam curves that are used for transition between a varying-focal-length fixing range and the zooming range, zooming parameters and focusing parameters are determined for their appropriate distribution. This causes a difficulty in ensuring a sufficiently balanced cam configuration to conduct a smooth zooming-focusing transition, resultantly necessitating to alter a rotation angle of the focusing cams or to compensate for transforming motion by the focusing cam.
In some prior art high power zoom lens, a focusing lens is simultaneously angularly and linearly moved in both the cases of the zooming and the focusing. Since guide grooves defined in a focusing cam barrel are configured so as to work as cams suitable to rotate the focusing lens, manipulation pins fitted in the guide grooves slide in and along the guide grooves in the focusing cam barrel during the zooming so as to rotate the focusing lens, and thus, a zooming manipulation permits the focusing lens to alter its direction to rotate so that a working zone with the focusing cams is shifted, thereby appropriately displace the focusing lens in any of the zooming ranges (see Patent Document 1 listed below).
However, it is still hard to ensure a sufficient displacement of the focusing lens to enhance the photographing performance at the minimum object distance and/or to inhibit from varying a focal length throughout the entire zoom range. Some other prior art zoom lens of high power not more than ×5 is of five-layer assembly where a first cam barrel is disposed inside a fixed barrel while a second cam barrel, a linear-shuttle barrel, and, a third cam barrel are located outside the fixed barrel and such a zoom lens has a drawback that its outer diameter cannot be reduced any further.
In other prior art high power zoom lens, focus correcting cams are located in the same rotary member as the focusing cams are, thereby attaining an appropriate displacement of the focusing cams (see Patent Document 2 listed below). With this mechanical design where the focusing lens is linearly displaced during the zooming, however, a fixed corrected displacement is applied in any of the zooming ranges, and this fixed corrected displacement makes it inappropriate to further shorten the minimum object distance in any of the zooming ranges for the high power zoom lens. Additionally, the high power zoom lens is also of five-layer assembly where first and second cam barrels, a linear-shuttle barrel, and a third cam barrel are disposed outside a fixed barrel, and such a zoom lens is disadvantageous in that its outer diameter cannot be reduced any further.
Some other prior art high power zoom lens, as shown in FIGS. 10 and 11, is comprised of a zooming relay ring 14 inside a fixed barrel 12, a first cam barrel 16 inside the zooming relay ring 14, and a focusing cam barrel 20 inside a linear-shuttle barrel 18 further inside the first cam barrel 16. The first cam barrel 16 is coupled to the zoom relay ring 14 with zooming relay studs 40 intervening therebetween, so that rotations of a zooming ring 30 are transmitted to the first cam barrel 16. The first cam barrel 16 includes 1st-cam-barrel guiding cams to fit on 1st-cam-barrel guiding studs 39 to slide the first cam barrel along the optical axis, 3rd-lens-group guiding cams to fit on 3rd-lens-group guiding studs 43, and 4th-lens-group guiding cams to fit on 4th-lens-group guiding studs 45. The first cam barrel 16 is also provided with 2nd-cam-barrel relay studs 50 that protrude outward ahead of the fixed barrel 12 and opposite to a lens mount 10. The 2nd-cam-barrel relay studs 50 are to fit in circumferential guiding grooves defined in the second cam barrel 22 (see Patent Document 3 listed below).
The above-mentioned high power zoom lens includes the zooming relay ring 14 inside the fixed barrel 12, the first cam barrel 16 inside the zooming relay ring 14, and the linear-shuttle barrel 18 inside the first cam barrel 16. The first cam barrel 16 is coupled to the zooming relay ring 14 with the zooming relay studs 40 intervening therebetween so that rotations of the zooming ring 30 are transmitted to the first cam barrel 16. In order to slide the first cam barrel 16 along the optical axis, the first cam barrel 16 must have its 1st-cam-barrel guiding cams fitted on the 1st-cam-barrel guiding studs 39, its 3rd-lens-group guiding cams fitted on the 3rd-lens-group guiding studs 43, and its 4th-lens-group guiding cams fitted on the 4th-lens-group guiding studs 45.
However, the first cam barrel 16 has its entire length restricted along the optical axis while the 1st-cam-barrel guiding cams, and the 3rd- and 4th-lens-group guiding cams are all defined in a layout with restrictions of their respective axial extensions imposed. Especially, for attaining a more enhanced zoom ratio, an axial displacement of third and fourth lens groups are to be greater, but it is hard to implement a well-balanced disposition of the guiding cams for these lens groups to be confined within the axial dimension available in the first cam barrel 16. More specifically, with an awkwardly constrained layout of the guide cams, more restrictions would be imposed on configurations and positions of the guide cams to leave only a captive room for design.
In addition, for the available entire length of the fixed barrel 12, a stroke of the linear-shuttle barrel 18 is elongated as the displacement of the third lens group becomes greater, and an amount by which the linear-shuttle barrel 18 is superposed on the fixed barrel 12 for the tele-photo shooting, namely, an overlapping segment is reduced so that the required stability of the lens barrel is no longer ensured.
Patent Document 1: Japanese Patent Unexamined Publication No. H8-304684
Patent Document 2: Japanese Patent Unexamined Publication No. 2000-89086
Patent Document 3: Japanese Patent No. 3689379
The present invention is made to overcome the aforementioned disadvantages of the prior art zoom lens barrels, especially, the prior art inner focusing zoom lens barrels, and accordingly, it is an object of the present invention to provide an improved inner focusing zoom lens barrel provided with cams of a well-balanced configuration for smooth zooming and/or focusing operations.
It is another object of the present invention to provide an improved inner focusing zoom lens barrel that attains a satisfactory photographing performance at the minimum object distance, that is capable of inhibiting a focal length from varying throughout the entire zoom range, and that has a reduced outer diameter.
It is still another object of the present invention to provide an improved inner focusing zoom lens barrel that has reduced restrictions on configurations and positions of guiding cams, that has a greater overlapping segment where a linear-shuttle barrel is superposed on a fixed barrel for the tele-photo shooting, so as to attain an enhanced stability.